Liquid crystal display units (liquid crystal display devices) are plane display devices having excellent features such as high resolution, thin thickness, light weight, and low-power-consumption. Because of recent improvements in display performance and a production capacity, and of an increased price competitiveness against other display devices, a market of the liquid crystal display devices has been rapidly expanded. Under these circumstances, there has been proposed a liquid crystal display device of a VA (vertical alignment) mode for improving contrast ratio and a viewing angle characteristic.
According to the liquid crystal display of the VA mode, liquid crystal molecules filling a gap between substrates are oriented substantially perpendicular to surfaces of the substrates while no voltage is applied. In this state, a polarization plane of light entered the liquid crystal display device is scarcely twisted in a liquid crystal layer. On the other hand, while the voltage is applied, the liquid crystal molecules are oriented at a certain angle with respect to a direction perpendicular to the surfaces of the substrates. The angle at which the liquid crystals are oriented depends on intensity of the voltage applied. In this state, the polarization plane of the light entered the liquid crystal display device is twisted in the liquid crystal layer. That is, by arranging two polarizing plates, one of which is provided on a light-entering side and the other one of which is provided on a light-emitting side, in such a manner that polarization axes of the two polarizing plates are in a crossed Nicols state, it is possible to achieve a normally black display in which a black display is performed while no voltage is applied whereas a white display is performed while the voltage is applied.
Such a VA mode achieves better contrast and viewing angle characteristic as compared to, for example, a TN mode. However, in a case where a gray level is displayed, the VA mode still has a problem that a display condition depends on a viewing angle. In order to overcome this problem, for example, Patent Literature 1 discloses a liquid crystal display device of an MVA (Multi domain Vertical Alignment) mode, in which a plurality of regions are provided within a pixel and the liquid crystal molecules provided in each of the plurality of regions are aligned at a different angle from each other.
Such a liquid crystal display device is arranged so that the liquid crystal display of the VA mode, in which a conventional vertical alignment film is employed and negative liquid crystal is enclosed as a liquid crystal material, further includes domain controlling means for achieving a state where the liquid crystal molecules within one pixel are oriented at a plurality of angles when the liquid crystal molecules are tilted.
(a) to (c) of FIG. 12 are cross-sectional views illustrating an example of a liquid crystal display device, in which the domain controlling means is provided. The example shown in FIG. 12 is arranged such that a liquid crystal layer is held by two substrates facing each other, and includes: an electrode 52 provided on an upper substrate; an electrode 53 provided on a lower substrate; projections 60 provided on inner surfaces of the electrode 52 and the electrode 53; and vertical alignment films 62 provided so as to cover the projections 60, the electrode 52, and the electrode 53.
As illustrated in (a) of FIG. 12, while no voltage is applied, the liquid crystal molecules are aligned perpendicular to surfaces of the two substrates due to an effect of the vertical alignment films 62. Since the liquid crystal molecules in the vicinity of the projections 60 are also to be aligned perpendicular to slanted surfaces of the projections 60, the liquid crystal molecules in the vicinity of the projections 60 are aligned obliquely to the surfaces of the two substrates. Nevertheless, almost all the liquid crystal molecules other than those in the vicinity of the projections are aligned perpendicular to the surfaces of the two substrates while no voltage is applied. As such, the black display is performed.
In contrast, while the voltage is applied, potential is distributed within the liquid crystal layer as illustrated in (b) of FIG. 12. That is, the potential in regions in which no projection 60 is provided is distributed in parallel with the two substrates (electrical field is in perpendicular to the two substrate), whereas the potential in the vicinity of the projections 60 is distributed obliquely to the two substrates.
The liquid crystal molecules are oriented depending on intensity of the electrical field while the voltage is applied. However, since the electrical field is perpendicular to the two substrates, the liquid crystal molecules can be oriented along any direction in 360 degrees with respect to the electrical field unless an orientation direction is set by rubbing.
Here, if some of the liquid crystal molecules are obliquely aligned in advance due to an effect of the projections 60 (see (a) of FIG. 12), the liquid crystal molecules in the vicinity of the some of the liquid crystal molecules are also aligned obliquely in a same direction as the some of the liquid crystal molecules. This is a characteristic that the liquid crystal molecules have. Further, the electrical field is distributed obliquely according to the slanted surfaces of the projections 60 in the vicinity of the projections 60 (see (b) of FIG. 12). Although negative liquid crystal molecules are oriented in a direction perpendicular to the electrical field when the voltage is applied, the direction is equal to a direction in which the negative liquid crystal molecules are originally aligned due to the effect of the projections 60. That is, the negative liquid crystal molecules are to be oriented in the direction more stably.
Accordingly, with the projections 60 provided as shown in (c) of FIG. 12, it is possible to achieve a state where the liquid crystal molecules are stably oriented in an intended direction in each region defined by the corresponding projection 60. This is due to an alignment effect attributed to the slanted surfaces of the projections 60 and obliquely distributed electrical field in the vicinity of the projections 60. When the voltage of a higher intensity is applied, the liquid crystal molecules are oriented in substantially parallel to the two substrates. With such an arrangement, it possible to control an orientation direction of the liquid crystal molecules in each region separated by the domain controlling means while the voltage is applied. As such, it is possible to achieve a better viewing angle characteristic while the gray level is displayed.